Final answer:
A change of color is the indicator that most likely suggests a chemical change is taking place, as it denotes the formation of a new substance with different properties.
Step-by-step explanation:
The indicator that most likely suggests a chemical change is taking place is a change of color. When a substance undergoes a chemical change, its molecular structure is altered, resulting in the formation of new substances with different properties.
A change in color is a visual clue that this has occurred. Other indicators include temperature changes, light emission, bubbles formation (when the substance is not boiling), and the formation of a solid product known as a precipitate. These changes are often more challenging to reverse compared to physical changes where the identity of the substance remains the same.